Can A child under 18 use infinity free services under a provisition of parent 18+

Welcome to the forum. The T&C’s are quite clear on this: A child under the age of 18 cannot have their own account. But that said, if you, as a parent had an account, and your child then built a site, and you hosted it here for them, to help them learn… In my opinion that would be ok. But I’m not the owner so you’d have to wait on admin to be certain.